Replicated Loci of the Human pMCH Genes: Antisense Expression and Potential for Homologous Recombination




Christine L. Miller*,

Margit Burmeiser and Robert C. Thompson

University of Michigan, IL

The pro-melanin concentrating hormone

(pMCH) gene has a feature common to many peptidergic genes, i.e.

the production of a peptide precursor molecule that is then

processed into more than one peptide. However, an additional

layer of complexity exists for the human pMCH gene, located on

chromosome 12q23.1. A 700 bp region of highly homologous sequence

is found in two other sites in the genome, one on 5p14 (pMCHL1)

and the other on 5q13 (pMCHL2). Transcription studies of the

three loci were made possible by radiation-hybrid mapping with

PCR-SSCP and then determining sequence differences between the

two human-variant pro-melanin-concentrating hormone-like genes.

To evaluate the transcription of each locus, we utilized pMCH or

pMCHL-specific primers in RT-PCR of total RNA isolated from human

hypothalamic tissue. The precise identity of the RT-PCR products

was determined by sequencing. A very substantial component of

human pMCH expression was shown to be antisense in orientation.

PMCHL expression was confirmed only for the pMCHL1 locus on 5p14,

and was determined to be unspliced and exclusively antisense in

orientation for a range of RT-PCR primers used. Production of MCH

peptide from the pMCHL loci was effectively ruled out in the

human hypothalamus, whereas production of MCH peptide from the

authentic pMCH locus on 12q would be expected to occur based on

the presence of appropriately spliced sense transcript. It is

possible that the pMCHL1 antisense transcript is involved in

regulation of the pMCH sense RNA. These results are discussed in

the context of the potential for viral-stimulated homologous

recombination between the replicated loci.